My 3116s usually reach temps of 185 at cruise. Yesterday, the stbd engine went above that and reached 195. It never went above that, but it did go down when at idle. I haven't looked into the issue yet, but I first plan to open the strainer to look for any clogs. Other things to note:

- The impellers were replaced in April, but I will open the cover to confirm that it's still in good shape.
- Last month my mechanic used a scope to look into the heat exchangers and while they weren't perfect, they weren't bad either. We made a plan to change the coolant, replace the thermostat and clean the heat exchangers during the off-season.
- I'll have to go back and look through the POs records, but as of now, I have no idea the last time the thermostat was replaced.

Can I simply pull the thermostat to inspect it? If so, what sort of signs should I be looking for?

If you are using Caterpillar ELC, then the chances of the thermostat being bad or clogged up is slim. They usually stick open or closed when t hey go bad and the symptoms would be entirely different that what you are seeing.

When the temperature hold at 180-185˚ then all of a sudden and for no apparent reason begins to creep up as load increases, but then returns to normal levels when you back off on the throttles, the problem is more likely inadequate water flow or inadequate heat exchange. Check the strainers.........something as simple as a potato chip bag can cause what you are seeing, then check the impellers since it is easy to do, then run the boat again and, if the temp continues to rise, be thinking about descaling the heat exchangers now rather then waiting for your off season.

Also, 205˚ is the limit.......while this is going on, do not let the temperatures exceed 205˚. Diesels do not tolerate overheating well. Some of t he engine parts are massive and the expansion at high temps is more than heads, head gaskets, cylinder liners, etc. can stand. At 200˚ begin slowing down until the temps stabilize at normal levels.

If you are using Caterpillar ELC, then the chances of the thermostat being bad or clogged up is slim. They usually stick open or closed when t hey go bad and the symptoms would be entirely different that what you are seeing.

When the temperature hold at 180-185˚ then all of a sudden and for no apparent reason begins to creep up as load increases, but then returns to normal levels when you back off on the throttles, the problem is more likely inadequate water flow or inadequate heat exchange. Check the strainers.........something as simple as a potato chip bag can cause what you are seeing, then check the impellers since it is easy to do, then run the boat again and, if the temp continues to rise, be thinking about descaling the heat exchangers now rather then waiting for your off season.

Also, 205˚ is the limit.......while this is going on, do not let the temperatures exceed 205˚. Diesels do not tolerate overheating well. Some of t he engine parts are massive and the expansion at high temps is more than heads, head gaskets, cylinder liners, etc. can stand. At 200˚ begin slowing down until the temps stabilize at normal levels.

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Thanks Frank. I also just spoke with my mechanic and his thoughts echo yours. One other thing he reminded me of was that we changed the belts last month too. He told me to check that the tension is still correct. I'll check all the simple things first and go from there.

You probably have 194˚ thermostats........as do I. My engines run at 195˚ and never get any higher. But, 205˚ is the back out of the throttles point.....never let these engines exceed 205˚.

John,

You have to use Caterpillar belts......NAPA, Dayton, etc do stretch a good bit. Cat belts will stretch some, but I usually check mine after bout 10 hours on a new set and they typically need to be tightened a bit, but never get so loose that the engine begins to heat up.

You have to use Caterpillar belts......NAPA, Dayton, etc do stretch a good bit. Cat belts will stretch some, but I usually check mine after bout 10 hours on a new set and they typically need to be tightened a bit, but never get so loose that the engine begins to heat up.

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Yes, I do have CAT belts. I checked them. They need to be tightened a bit, but they're not too bad. That is not the cause of this issue. I pulled the cover plate off the water pump and the impeller looks fine as I thought it would (it's only 3 months old). Strainer is clean, so it's not that. It's got to be the HE then. I'm going to buy some Barnacle Buster or similar product and run it through the HE and let it sit overnight. I'll see if that does anything. If not, I guess I'm draining coolant, cleaning the HE and replacing the t-stat. Good times.

I opened up the end cap of the HE. This is what it looked like. I guess this could do it. I used a coat hanger and a hose and cleaned it out the best I could. Now I need to go for a ride and see if it's any better.

That's not that bad John.
The area that really can't tolerate plugging on the raw water side is the gear oil cooler (but it does plug up) so you might consider inspecting it and circulating Barnacle Buster through the two coolers. There are tubes in that cooler you can't get to by rodding.
Also the CAT ELC if not changed per CAT requirements (I think it's every 7 years) it will form a gel on the engine cooling jacket surfaces and inhibit heat transfer. This requires a more "professional" flush.
Regarding poking steel wires in those brass tubes; I would be very careful that brass is soft. Use aluminum welding rod; it's softer than the brass.
Tom

I opened up the end cap of the HE. This is what it looked like. I guess this could do it. I used a coat hanger and a hose and cleaned it out the best I could. Now I need to go for a ride and see if it's any better.

I bought a 2000 480 Sedan Bridge on Lake Erie in Canada, and in July of 2016, I spent 2 weeks taking it down to Southport, NC. Once I was out in the ocean cruising at about 22 kts, the temperature jumped up and indicated that the engine was overheating, It seemed all the sudden, but only after the engines had been loaded for a while. My Nephew, Luke, first replaced the impeller while we were out at sea, and it made no difference. We then found a thermostat at Cape May, NJ, and headed there on one engine. In Cape May, we replaced the Thermostat, and again, after running for a few hours, the same problem reoccurred. We did not have a heat gun, so the next thing we then focussed on the temperature sensor. On the way to pick that up, which was somewhere near Oriental, NC, Luke noticed the the temperature cable looked crimped. He uncrimped the cable and the problem went away. We ended up replacing the thermostat anyway, but that was several days later. Other than the drama of the engine appearing to overheat, the trip was a lot of fun.